Sound film reproducing apparatus



p 1937- Q J. c. DAVIDSON 2,094,063

SOUND FILM REPRODUGING APPARATUS Filed Dec. 19, 1936 INVENTOR J. C. 0/1 V/DSON By TLUWM ATTORNEY Patented Sept. 28, 1937 'lTES PATENT ()FFlQE SOUND FILM REPRODUCING APPARATUS Application December 19, 1936, Serial No. 116,686

4 Claims.

This invention relates to sound film reproducing systems and more particularly to improvements in apparatus employed in such systems.

At the present time, the sound record portion of sound picture films for theater reproduction may bear either the present standard single track sound record or one of several sound records comprising two separate adjacent tracks. One sound record of the double track type is known as a push-pull sound record which consists of two separate adjacent tracks in which the two halfwaves of the sound wave are recorded 180 degrees out of phase. Another sound record of the double track type is known as a stereophonic sound record in which the separate adjacent tracks represent the same sound waves as recorded from different positions with respect to a single sound source. A further record of this type is known as a split frequency record in which each track is a record of sound frequencies within a certain frequency band included in the recorded sound.

To reproduce from the present standard single track sound record only one light sensitive element in a reproducing circuit is necessary. However, in reproducing from a double track sound record, it is necessary that each record be projected to a separate light sensitive element and that these light sensitive elements, in the case of a push-pull sound record, be connected in push-pull arrangement with a current responsive device in the reproducing circuit. Present standard theater reproducing apparatus is not capable of reproducing a double track sound record and to provide separate sound reproducing apparatus for the reproduction of this type sound record would obviously be impractical from a commercial standpoint. It is therefore desirable that theater sound film reproducing apparatus be capable of reproducing either a double track sound record or the present standard single track sound record.

It is the object of this invention to provide a sound film reproducing apparatus capable of reproducing either standard single sound track or double track sound records.

A feature of the invention lies in the provision of means whereby the transfer from one type of reproduction to the other may be readily effected without altering the position or adjustment of the essential electrical and optical elements of the reproducing system.

A further feature of the. invention lies in the provision of a single control means for producing operation of all the elements necessary in the transfer from one system of reproduction to the other.

The invention will be more readily understood by reference to the accompanying drawing in which:

Fig. 1 is a side elevation of the sound reproducing portion of a sound picture reproducer disclosing the interior of the film driving compartment and the photoelectric cell compartment;

Fig. 2 is a view, partly in section taken through line 22 of Fig. 1;

Fig. 3 is a section taken through line 33 of Fig. 2; and

Fig. 4 discloses a preferred form of circuit for coupling the photosensitive element to a reproducing circuit for the reproduction of a push-pull sound record.

Fig. 1 discloses the sound reproduction portion of a sound picture reproducing apparatus comprising a compartment I, which houses the film driving mechanism and a compartment 2, which houses the photoelectric cell and the elements included in the photoelectric cell coupling circuit to the reproducing apparatus. Compartment I contains a constant speed film driving sprocket 3 and a take-up sprocket 4, both driven from a motor M by means of suitable gearing, not shown. Pivoted film retaining rollers 5 and 6 insure engagement of film F with the sprockets 3 and 4 respectively. Numeral 1 denotes a freely rotatable film engaging drum which is secured to a shaft, the other end of which supports a suitable flywheel (not shown). roller 8 retains the film F on the drum 7.

The film F is fed from a picture projecting compartment 9 of the apparatus to the sound reproducing compartment where it engages in succession the film-driven drum '1, sprocket 3 and sprocket 4. Rotation of the drum 7 and its asso ciated flywheel is produced by movement of the film F in response to the driving action of sprocket 3. The film may be adjusted laterally by means of roller 8 so that the marginal edge of the film bearing the sound track will overhang one edge of the drum 1. The film F is fed from the takeup sprocket 4 to a take-up reel located in a reel housing In.

A lamp l 3 is secured in an adjustable mounting M in compartment I. A combination condenser lens and double prism unit I 5 projects light rays from lamp l3 to the over-hanging edge of film F on the roller 1. The unit l5 includes one prism which deflects the light rays inwardly toward the rear wall of housing I and a second prism which deflects these light rays to the overhanging sound record portion of the film F on roller 1. Lenses located in a lens tube l6 project a magnified Pivoted film retaining image of the sound record to a fiXed slit in slit assembly ll. A photoelectric cell l8 receives the record modulated light rays projected through the fixed slit in slit assembly ll.

While applicant mentions various types of double track sound records capable of use on sound picture films for theater reproduction, his drawing discloses a reproducing circuit and switching arrangement to be employed in a sound reproducing system for the reproduction of a standard single sound record or a push-pull sound record. His invention, however, may be applied to reproducing systems in which reproduction is obtained from a standard single track sound record and any or all of the double track records mentioned above. Suitable coupling circuits and switching arrangements may be provided for coupling the two photosensitive elements in parallel to a single current responsive device and for coupling each photosensitive elements to a separate eurrent responsive device included in separate reproducing channels for the reproduction of stereophonic and split frequency sound records. l 1 k In the reproduction of a standard single rack sound record, the image of the single film record is projected to a single light sensitive element. However, the push-pull sound record consists of two adjacent records located in the same film area as the single standard record and each of these separate records must be projected to a separate light sensitive area. Two separate photoelectric cells may be used and means may be provided in the form of deflecting prisms between the film and the cells for deflecting each record image to a separate one of the photoelectric cells. The preferred arrangement, however, is to employ a double photoelectric cell contained in a single envelope.

Difiiculty has been encountered in obtaining distortionless reproduction from a double track sound record using either two separate cells or a double unit cell due to the projection of the light rays from one record onto the adjacent photosensitive area which should receive only light rays from the other record. This difiiculty is caused either by the slight transverse weaving of the film as it passes over the flywheel drum 7 or by slight misalignment of the sound record throughout the complete film length.

In accordance with this invention these difficulties are eliminated by providing means in the form of a mask 26 which may be moved into the optical system to mask a small area in the center of the light beam when reproducing a double track sound record. This mask 20, in this disclosure, is movably mounted in the slit assembly ll in a manner to be described.

In Figs. 1, 2 and 3 the slit assembly ll comprises a circular member 2! provided with an aperture 22. Member 25 is provided with grooves to receive slidable slit forming members 23 and 24. A second circular member 25 is provided with an aperture 25. Member 25 is also provided with a groove to receive the slidable. mask 20. Members 2i and 25 are held together as a unit by means of screws 27 (Fig. 2). The size of the slit may be adjusted by slit forming members 23 and 24 and these members may be held in adjusted position by means of set screws 28 and 29. The mask 25 has a slot 36 to provide clearance for the screw 29. The entire unit is mounted in an annular supporting member 3! having an integral arm secured to the inner wall of housing 2 by means of machine screws 32 (Fig. 1). The

slit assembly I! may be rotated in the holder 3| to provide for azimuth adjustment of the slit and may be held in adjusted position by means of a set screw 33 (Fig. 2) mounted in member 3|.

Fig. 4 discloses a circuit coupling the photoelectric cell l8 to a current responsive device in the input of a sound reproducing circuit. The current responsive device disclosed in the drawing is a transformer T. The photocell I8 preferably comprises two cathodes 34 and 35 and two anodes 36 and 3'! enclosed in a common envelope. Polarizing potential for the photocell is obtained from a potential source A.

A switch 38 provided in the coupling circuit permits the several elements of the double photoelectric cell Hl to be suitably connected to the primary of transformer T for either push-pull or standard reproduction. A switch blade 39 has conducting end portions and 4| separated therefrom by suitable insulating material. The switch blade is secured to a shaft 42.

As shown in Fig. 4 the switch is in position for standard reproduction. In this connection the two separate anodes 36 and 31 are connected in parallel to one side of the transformer primary and the mid-point connection of the upper half of the transformer primary is connected to the positive terminal of the potential source A. The cathodes 34 and 35 are connected to the negative terminal of potential source A. The circuit is from the positive terminal of potential source A, lead 45, upper half of primary of transformer T, lead 45, resistance 47, anode 36, cathode 34, lead 48 to the negative terminal of potential source A. Cathode 35 is connected through lead 48 to negative terminal of source A and anode 31 is connected to lead 46 through lead 49, switch contacts 50 and 5d and lead 52.

Operation of switch blade 39 in a clockwise direction connects the. separate anodes 36 and 31 to opposite sides of the transformer primary and the mid-point of the transformer primary to the positive terminal of the potential source A for push-pull operation. The circuit from the negative terminal of potential source A is through lead 48, cathodes 34 and 35, and anodes 36 and 3t. Anode 36 connects through resistance 41 and lead 46 to one side. of the transformer primary. Anode 3? is connected to the opposite side of the transformer primary through lead 49, contact 56, switch blade 4 I, contact 53, resistance 54 and lead 55. The switch blade contact 40 bridges contacts 56 and 51' of the switch to connect the mid-point of the primary of the transformer through lead 45 to the positive terminal of source A.

Resistances 58, 59 and 60 and condensers 6| and 62 constitute elements of a filter which furnishes the final filtering of the polarizing potential for the cell [8.

Referring to Fig 2, the switch 38 is mounted in the base of an enclosure 65. The switch shaft 42 extends through the upper wall of the enclosure 65 and is rotatable in a bushing 66 which is provided with an external screw thread to receive nut 61. The switch shaft 42 is provided with an operating arm 68 having a knurled handle 69 which extends through a small opening 79 in a removable partition II. The compartment 2 may be completely closed by a door 12 hinged at 13 (Fig. 1).

A sleeve 75 fits over shaft 42 and has a flanged end 1'6 which rests on nut 61. A nut 11 having a flanged portion 18 engages the externally threaded upper portion 19 of nut Bl to hold sleeve 75 in place. Sleeve 15 is provided with a cut-out portion (not shown) to give clearance to the operating arm 68. The upper end of member 15 is provided with a slot 80.

A sleeve 8| fits over sleeve 15. A pin 82 passes through the slot 80 in member 15 and has its ends secured in member 8L Member BI is provided with a spiral slot 83 through which the switch operating arm $8 extends. A mask engaging member 85 is adjustable along the upper end of member 8| and may be secured in adjusted position by means of set screw 86. Member 8| is provided with a groove 8'! to receive the lower flanged end of mask 20 (Fig. 3).

In the position shown in the drawing, both the reproducing optical and electrical systems are adjusted to reproduce from a standard single track sound record. Movement of the operating arm 68 to the left (Fig. 1) will produce clockwise movement of switch blade 39 to provide a pushpull connection between the photosensitive elements and the current responsive device in the reproducing circuit. The operating arm 68 in moving to the left will bear against the upper edge of spiral slot 83 in member 8|, which, being held against rotative movement by pin 82 in slot 80, will move Vertically upward to effect an upward movement of mask 29 into the area of the slit formed by members 23 and 24.

It is apparent from the foregoing that applicant has provided a sound picture projecting system in which the optical and electrical systems may be altered without effecting adjustment of the essential elements of each system to reproduce either single track or double track sound records and in which the number of operations necessary to effect a change from one system to the other is reduced to a minimum.

What is claimed is:

1. In a sound film reproducing system having means for projecting a beam of sound modulated light, in combination, a plurality of photosensitive elements disposed in the path of the beam projected by said means, means movable into said light beam to mask a portion thereof project-ed to said photosensitive elements, an electrical circuit including said photosensitive elements, a current responsive device and a switching means, and a common operating means for said masking means and said switching means.

2. In a sound film reproducing system having means for projecting a beam of sound modulated light rays, in combination, a photoelectric cell having a plurality of light sensitive elements disposed in the path of said light beam, an electrical circuit including said photoelectric cell and a current responsive device, means in said circuit for changing the circuit arrangement between said light sensitive elements and said current responsive device, means movable into said projected beam to mask the center portion thereof projected to said photoelectric cell, and a unitary control means for said switching means and said masking means.

3. In a 'sound film reproducing system, having means for projecting a beam of sound modulated light, in combination, a plurality of photosensitive elements disposed in the path of said beam, an opaque mask movable into the path of said beam to mask the center portion thereof, an electrical circuit including said photosensitive elements, a current responsive device, and a switch, said switch being operable to alternatively connect said photosensitive elements in parallel arrangement or a push-pull arrangement with said current responsive device, operating means for said switch, and means associated with said switch operating means for moving said masking means into the path of said projected light beam when said switch is operated to effect a push-pull connection between said photosensitive elements and said current responsive device and to withdraw said masking means from the path of said projected beam when said switch is operated to efiect a parallel connection between said photosensitive elements and said current responsive device.

4. The combination in a sound film reproducing system, means to project a beam of modulated light, a plurality of photosensitive elements disposed in said projected beam, means movable into said beam to mask a portion thereof, an electrical circuit including said photosensitive elements, a plurality of current responsive devices and a switching means, said switching means being operable to alternatively connect all said photosensitive elements in parallel with a single one of said current responsive devices or each photosensitive element individually to a separate one of said current responsive devices, and a unitary control means for said switching means and said masking means.

JOHN C. DAVIDSON. 

